The broad long term goal of this proposal is to determine at the subcellular level, the coupling between chemoattractant stimulus and migratory response of the human neutrophil. This migratory response is a result of the binding of a chemoattractant to its receptor and the start of a cascade of various reactions in different signal transduction pathways. The four specific Aims are motivated by contemporary questions and major uncertainties in the relationship between the mechanisms of signal transduction and the migratory response. The Specific Aims are: To characterize the coupling between chemoattractant-receptor binding and the rate of pseudopod extension; To study the role of chemoattractant gradient and absolute chemoattractant concentration in cell motility; To study the dynamics of adhesion receptor upregulation and shedding after activation by chemoattractants; and To study the role of the chemical environment on chemoattractant stimulated motility responses. The approach will be to measure and compare biochemical characteristics, such as receptor occupancy and Ca2+ mobilization, and migratory responses, such as the dynamics of pseudopod formation, adhesion receptor upregulation, and the dynamics of cell crawling. To do this, novel micropipet-based methods will be introduced where the above biochemical characteristics and migratory responses will be measured for single cells. Neutrophils in different states, stimulated by different chemoattractants, and in the presence of different signal transduction modulators, will be studied. These methods will provide measurements of fast changes of the migratory responses, their dependence on the local receptor occupancy, and the local chemical environment. The results from these studies will contribute to the understanding of the relationship between migratory responses and chemoattractant stimuli of the neutrophil. This will provide valuable information for developing means to control neutrophil motility, which is one of the essential immune functions.